Radiofrequency amplification system



Feb. 18, 1930. H. F. HARMON 1,747,297

RADIOFREQUENCY AMPLIFI CATION SYSTEM Filed Oct. 17, 1923 3 Sheets-Sheet 1 GRID VOLTAGE PLATE VOLTAGE /7 Inventor Attorney Feb. 18,1930 H. F. HARMON 1,747,297

RADIOFREQUENCY AMPLIFI CATION SYSTEM Filed Oct. 17, 1923 3 Sheets-Sheet 2 lnoentor maimwww Attorney Feb. 18, 1930. Y H. F.,HARMON V 1,747,297

RADIOFREQUENCY AMPLIFI CATION SYSTEM Filed 001;. 17, 1923 3 Sheets-Sheet 5 5 g -lllllllll 28 lnuentor Patented Feb. 18, 1930 UNITED STATES PATENT OFFICE HERBERT F. HARMON, OF GROVE CITY, PENNSYLVANIA, ASSIGNOR TO PERGIVAL D. LOWELL, OF JAMAICA, NEW YORK RADIOFREQUENCY AMPLIFICATION SYSTEM Application filed ()ctober 17, 1923. Serial No. 669,175.

My invention relates broadly to electron tube circuits for the amplification of electrical energy, and more particularly to a circuit arrangement for a radio frequency amplifier associated with radio receiving apparatus.

One of the objects of my invention is to provide an arrangement of electron tube circuits connected for amplification of incoming energy at radio frequency with means for neutralizing and suppressing undesired oscillations or reactions between different parts of the radio frequency amplification system.

Another object of my invention is to provide a radio frequency amplifier unit which may be utilized in association with standard constructions of radioreceiving sets for increasing the amplitude of the energy delivered to the input circuit of such a set.

A further object of my invention is to provide a circuit arrangement for a radio frequency amplifier having a multiple number of stages with a single control means connected with the several electron tube circuits for suppressing undesired oscillations in each 9,5 of the electron tube circuits.

Another object of my invention is to provide coupling means between the input and output circuits of a radio frequency amplification system for efiecting opposition between plate circuit voltage and grid circuit voltage normally having a phase displacement of 180 one from the other whereby undesired oscillatory reaction between the cir cuits may be gradually decreased and suppressed to a zero value, enabling amplification of desired frequencies while undesired oscillations are neutralized.

A further object of my inTention is to provide an apparatus unit in the form of a radio o frequency amplifier which may be added to present types of radio receivers including a detector and in some instances an audio frequency amplifier whereby an inductive trans fer of energy is effected between the output circuit ofthe radio frequency amplifier and the input circuit of the usual receiver for increasing the amplitude of the signals in the telephones or reproducer.

Still another object of my invention is to provide means in a radio frequency amplifier whereby relatively large inductances may be employed for interlinking a plurality of tube circuits with a relatively large inductance in the output circuit of the last tube of the amplifier for creating a field of force of sufficient area and intensity to interlink the circuits of the usual receiver placed in proximity of the radio frequency amplifier whereby the energy which would normally operate the usual receiving circuit is multiplied many times by the operation of the radio frequency amplification system.

My invention will be more clearly understood from the following specification by reference to the accompanying drawings, in which:

Figure 1 is an elemental diagram representing the theory involved in my radio frequency amplification system and showing the method of coupling a radio frequency amplifier of my construction with the usual construction of radio reciver; Fig. 2 is a theoretical diagram of the relation of the grid and plate voltage of the electron tube circuit of a radio frequency amplifier, which phenomena is involved in my present method for suppressing undesired oscillation in radio frequency amplification circuits; Fig. 3 is a diagrammatic arrangement illustrating the relatively large inductance which may be employed for interlinking the output circuit of my radio frequency amplifier unit with the input circuit of a detector without undesired oscillations within-the radio frequency amplifier system; Fig. 4 illustrates the application of my invention to three stages of radio frequency amplification in an apparatus unit which is added to an ordinary radio receiving apparatus for increasing the amplitude of the signals reproduced by such apparatus; Fig. 5 is a diagrammatic arrangement of a two stage radio frequency amplification system coupled with a detector and any desired number of stages of audio frequency amplification with means connected in the radio frequency amplification circuit for neutralizing oscillations in the system; Figs. 6, 7, 8, 9, and 10 show radio frequency amplification circuits with diflerent means introduced in the grid and plate circuits for inductivelyrelating the circuits in such manner that the phase differences between the plate and grid voltage is caused to operate to render the conditions of oscillation null; and Fig. 11 shows 1 loop receiver employing. the circuit of my invention.

Heretofore the advantages theoretically obtainable by the use of radio frequency amplification have not been readily obtained in practice by reason of the tendency of the sevoral circuits in the radio frequency amplifier to oscillate and render reception either impossible or cause distortion of the reproduced signal. By my present invention I eliminate undesired oscillations and reaction in radio frequency amplifiers and thereby provide an apparatus unit for effectively increasing the amplitude of incoming signal energy. I am enabled to utilize in the output circuit of the radio frequency amplifier a relatively large inductance having such flux interlinkages of area and intensity that the complete apparatus unit may be positioned adjacent anordinary receiving set and energy inductively 'ransferred from the radio frequency ampliication unit to the receiving set with a marked increase in amplitude of the reproduced sig nal. The ordinary receiver which may be of the regenerative type need have no change whatsoever in the internal circuit arrangement. The antenna-ground connections are removed from the receiver and the terminals connected by means of a short circuiting link, forming a radio frequency energy pick-up circuit with reference to the output of the radio frequency amplifier. Antenna-ground connections may then be connected to the inputcircuit of the radio frequency amplification system and all of the inherent advantage of increased signal strength obtained in the usual receiving circuit.

In radio frequency amplification circuits utilizing a number of electron tubes, the plate voltage is 180 out of phase with the grid voltage. I utilize this fact for the suppression of undesired oscillations by introducing in inductive relation with the grid input inductor a plate inductor in such relationship that the flux in the grid inductor may be gradually suppressed and actually decreased to substantially zero. This phenomenon is used in the present circuit arrangements to such a degree as to stabilize the radio frequency amplifier circuit so that the conditions of oscillation will be made null, 'athough the desired signal frequency is amplified for delivery to the detector circuit.

Referring to the drawings, Fig. 1 illustrates an electron tube 1 having grid electrode 2, filament electrode 8, and plate electrode 1 conncctedin a circuit arrangementfor radio frequency amplification. Radio frequency energy isdelivered to'the input circuit of the amplifier by means of coil 5. The grid input inductor -6 is inductively coupled-with coil 5 and the input circuit is tuned to the desired frequency by means of condenser 7 A relatively large inductance 8 is connected in the plate circuit of the radio frequency amplifier. In order to eliminate the tendency of retransfer of energy from the plate circuit to the grid circuit with inherent undesired regeneration, reaction, and oscillations, I provide a plate inductor 9'which is relatedto-the grid inductor 6 in such manner as to oppose any retransfer or reamplification with the resultant effect of suppressing oscillations and stabilizing the operation of the radio frequency amplifier. The filament electrode 3 is heated from a suitable source such as 10, and the plate is positively charged from a suitable source such as 11. I am enabled to employ a relatively large inductance 8 in the plate circuit in the output circuit of the radio frequency amplifier without oscillations. The usual radio receiver 12 involving any type of receiving circuit but including a tuning system may be placed in proximity of' the inductance 8 and energy transferred inductively from the radio frequency amplification circuit to the tuning circuit 14. The antenna and ground terminals on the receiver are connected by means of a'shortcircuiting link, as represented at 15, forming an inductive radio frequency energy pickup circuit. With this arrangement of apparatus it Will be understood that a radio frequency amplifier unit may be added to any of the usual types of'radio receivers by merely connecting the radio frequency energy collecting-circuit to the input of the radio frequency amplifier and p0- sitioning' the amplifier unit adjacent the receiver unit, so that the magnetic field of the inductor in the output circuit of the radio frequency amplifier unit interlinks with the inductance in the input circuit of the receiving apparatus. When the short circuiting link 15 is in place, the pick-up circuit formed by the radio receiver unit 12 comprises the link 15. terminal A, inductance 14 and terminal G, tuned by means of a variable condenser normally in the antenna lead to the radio receiver unit.

In Fig. 2 the voltage characteristic in the grid circuit of the radio frequency amplifier tube 1 is represented at 16. The plate voltage characteristic is represented at 17 as being 180 out of phase with the grid voltage. By introducing the opposed inductive relationship between the grid and plate circuits these voltages are oppositely related and cause the suppression of oscillations.

In Fig. 3 I have shown a single stage of radio frequency amplification in association with an electron tube detector circuit. An antenna 18 is connectedv to an aperiodic primary winding 5 and the circuit completed to ground 20. The primary winding5. has been numbered similarly to the corresponding Winding in Fig. 1. The windings are suitably inductively related 011 a coil support 19. Coil 6 is positioned in proximity of coil 5 and connected to the input circuit of the radio frequency amplifying tube 1. The neutralizing inductor 9 is adjustably positioned on shaft 21 in proximity to the grid inductor 6. The plate inductance 8 is relatively large and is mounted on coil support 22 carrying coil 23 which connects to the input of the detector circuit 24 operating the signal responsive device 25. The plate inductor 8 may be widely separated from grid inductor 23 so that greater selectivity may be attained. The separation or coupling may be adjusted to the optimum coupling (K) giving greatest selectivity and signal strength as indicated by formula:

in which:

R =radio frequency resistance of plate inductor,

R =radio frequency resistance of grid inductor,

o=2w frequency being received,

M=mutual inductance.

This wide coupling which is possible between the grid and plate inductors results in great selectivity and is especially good in eliminating shock excitation from nearby key clicks of powerful continuous waves transmitters.

In Fig. 4 I have illustrated the method of suppressing oscillations in a three stage radio frequency amplifier. An antenna ground circuit 185262O is provided or some other form of radio frequency energy collecting circuit may be employed connected with the input circuit of the radio frequency amplifier consisting of electron tubes 27, 28, and 29. Each of the tubes includes input and output circuits with coupling coils of relatively large inductances 30, 31, 32, 33, and 34 connected in the several circuits as shown. A coupling inductor 35 is connected in the input circuit of each of the electron tubes. A neutralizing inductor 36 is connected in each of the plate circuits of the several tubes and adjustably coupled with coil 35. Each of the input circuits of the several tubes may be tuned separately or all simultaneously in a group by a mechanical arrangement of variable condensers 37, 38, and 39. A source 40 has been shown for heating the several filament electrodes, and a high voltage battery 41 is shown for supplying plate potential for the several tubes of the series. The complete radio frequency amplifier and tuning system is represented as enclosed by lines 42. The ordinary receiver 12 which may be of the regenerative circuit type has its tuning system moved in the proximity of the coupling coil 34 in the output circuit of the last stage of the radio frequency amplifier with a shunt connection across the antenna and ground terminals. Energy is now picked up from the output circuit of the radio frequency amplifier by the pick-up circuit formed in the receiver for obtaining a response of substantial audibility in reproducer 25.

In Fig. 5 I have shown a two stage radio frequency amplifier consisting of tubes 27 and 28 coupled by inductances and 31. The coupling inductor is connected in the input circuits of the tubes and the neutralizing inductor 36 is connected in the output circuits of the tubes. A detector 24 may be coupled to the inductance 32 through inductance 23 and the rectified energy delivered to an audio frequency amplifier which may comprise tubes 42 and 43 which deliver the amplified energy to the reproducer 25. In Figs. 4 and 5 the secondary windings are illustrated poled to their respective primaries in such manner that oscillations in the several tube circuits may be suppressed.

The neutralizing inductor maybe fixed in position with relation to the grid inductor 6 as represented in Fig. 6, and oscillations'suppressed by varying the neutralizing flux by increments. Taps 44 may be provided on the neutralizing voltage value for suppressing oscillations in the radio frequency amplifying circuit.

In Fig. 7 I show a different method for varying the neutralizing voltage by adjustably positioning a copper disc 46 in the field of the neutralizing inductor 9. The copper disc 46 may be rotated to dotted line position 47 by means of shaft mounting 48 for changing the coupling. The coil 9 is so coupled to coil 6 that it functions at all frequencies which the circuits are designed to receive to suppress oscillations in tube 1. High frequency eddy currents are induced in the copper disc 46 by its location within the magnetic field of Winding 9 which eddy currents will have a maximum value when disc 46 is perpendicular to the direction of the turns of coil 9 or parallel to the axis of the coil as is shown in dotted line position, and a minimum value when the disc 46 is edgewise or in full line position, thereby reducing the plate current energy andthe tendency of the tube or tubes to oscillate. V

The neutralizing inductor may be coupled to the coupling inductor in various ways. In Fig. 8 I have illustrated the coupling inductor 35 connected in the grid'circuit of the radio frequency amplifying tube 1 with the neutralizing inductor 36 adjustably coupled thereto. In Fig. 9 the coupling inductor 35 is connected in the input circuitadj acent the filament electrode of the radio frequency amplifying tube 1 and the neutralizing inductor 36 adjustably coupled therewith. In Fig. 10 I have illustrated the neutralizing inductor 36 coupled With the primarywi-nding 5 of'the antenna'ground-circuit 18 n c manner: as to suppressundesired oscillations.

In Fig, 11 I. have shown how the grid and plate inductors and 36 are arranged in a loop receiring circuit wherein the incoming signals are receivedaby coil antenna tuned by condenser 46.

Inthe operation of my radio frequency amplificationsystemit will be observed that in a plurality-of stages of electron tube radio frequency amplification that the voltage relatioirof each plate is in the same direction or'angle. The voltage relation of each grid isalso in thesame direction or angle. Each tube oftheseries can be so adjusted that each has the same tendency to oscillate.

Therefore, lay-introducing a common neutralizing voltage fromv each plate in the inductor 36 and couplingitwith a common grid inductor 35in the proper phase relation, each tube can be controlled as desired by a single control. In the arrangement of circuits illustrated the coupling bet-,weenthe coupling coil 35 in the neutralizing coil 36 is adjusted to a point where undesired oscillations are suppressed. By employing this radio frequency amplifying system with the usual radio receiver, the receiver becomes more-sensitive and selective. In the case of a single circuit regenerative receiver the undesired. reradiation from the antenna is suppressed, thereby usefully emplaying the relatively inexpensive single circuit radio-receiver in a manner which prevents interference with receivers operating in close proximity thereto. My arrangement of .circuitsalso provides a very effective method of controllingthe vigorousness of oscillation of the radio frequency amplifying tube, thusenabling. very satisfactory reception of continuous wave signals by the heat recep-- tion method, with the radio frequency amplifying tubes furnishing the beat signal voltage.

While I have illustrated my invention in certain particular embodiments, it is to be understood that various modifications may he made. For example, my method of neutralizing. oscillations. may. also be applied in reflex circuits withimarked success and with :out distortion of the received signal during either radio or audio frequency amplification processes. I intend no limitations upon the lIHZGDtiOILOtllGI. than are imposed by the scope of the appended claims.

WhatI claim and desire to secure by LettersPatfint of the United States is as follows:

1. Radioreceiving appa atu mp n a; plurality of electron tubes each having grid, cathode and plate electrodes, input and output circuits in er onn t g aid trodes, means coupling said circuits in cascade, differential balancing apparatus for regula ing the-operation of sa d circu t sa .difierentia'lbalancing appa us c mpr sing of; windings. connected in opposition,

with one of said windings connected in circuit with the plate electrodes of each of said tubes and the other. of said windings connected in circuit with the grid electrodes of each of said tubes, said windings being mutually adjustable for controlling the amplification properties of all of said circuits simultaneously.

2. An amplification system comprising a plurality of electron tubes each having grid, cathode and plate electrodes, input and output circuits interconnecting said electrodes and coupled in cascade, and means for controlling the regenerative condition of said circuits simultaneously comprising a device having two mutually associated impedance elements, with one of said impedance elements connected in common with each of said output circuits and the other of said elements connected in common with each of said input circuits and oppositely effective upon each other for simultaneously regulating the am plification properties of said system.

HERBERT HABMON. 

